1. Technical Field of the Invention
The present invention relates generally to tire pressure monitoring systems for vehicles. More particularly, the invention relates to a remote tire pressure monitoring system for a vehicle, which includes a plurality of tire monitors configured to operate in a power saving mode and can provide a reliable and almost real-time monitoring of the inflation pressure of tires of the vehicle.
2. Description of the Related Art
A remote tire pressure monitoring system for a vehicle, such as disclosed in U.S. Pat. No. 5,602,524, generally includes a plurality of tire monitors and a receiver.
Each of the tire monitors is installed on one of a plurality of wheels of the vehicle and includes a pressure sensor and a transmitter. The pressure sensor works to sense the inflation pressure of a tire fitted on the wheel. The transmitter works to transmit a pressure transmitting signal that contains information on the inflation pressure of the tire sensed by the pressure sensor.
The receiver is installed on the body of the vehicle. The receiver is configured to receive the pressure transmitting signals transmitted from the tire monitors, determine the inflation pressure of the tires based on the information contained in the received pressure transmitting signals, and perform various processes based on the determined inflation pressure of the tires, such as informing the vehicle driver of the determined inflation pressure of the tires via a display device.
In such a remote tire pressure monitoring system, each of the tire monitors is generally supplied with electric power by a battery provided on the same wheel. In order to secure a long service life of the battery while decreasing the size (i.e., the capacity) of the same, it is required to decrease the power consumption of the tire monitor.
To meet the above requirement, there have been proposed three approaches.
The first approach is to decrease the power consumption of an IC (Integrated Circuit) employed in the tire monitor by advanced process technology.
However, in general, the majority of the total power consumption of the tire monitor is caused by transmission of the pressure transmitting signal, whereas only a minority of the same is caused by the IC. Therefore, even if the power consumption of the IC is ultimately minimized, this will be still not enough to decrease the total power consumption of the tire monitor to a satisfactory level.
The second approach is to reduce the number of transmissions of the pressure transmitting signal by employing a running detection device (e.g., an acceleration sensor). Specifically, the running detection device is employed to provide the tire monitor with information on whether the vehicle is running or at a standstill; thus, the tire monitor can transmit the pressure transmitting signal only when the vehicle is running, thereby reducing the number of transmissions of the pressure transmitting signal.
However, to timely provide the receiver with the information on the inflation pressure of the tire, it is desirable for the tire monitor to periodically transmit the pressure transmitting signal at sufficiently short time intervals when the vehicle is running. Thus, with the second approach, there is a limitation to reduce the number of transmissions of the pressure transmitting signal and thus a limitation to decrease the power consumption of the tire monitor.
The third approach is to reduce the number of transmissions of the transmitting signal by employing a triggering device. Specifically, the triggering device is installed on the body of the vehicle and works to transmit a trigger signal; the tire monitor further includes a receiver to receive the trigger signal. When the receiver requires the information on the inflation pressure of the tire, the receiver controls the triggering device to transmit the trigger signal, which triggers the transmitter of the tire monitor to transmit the pressure transmitting signal.
Since the pressure transmitting signal is transmitted only when the receiver requires the information on the inflation pressure of the tire, the number of transmissions of the pressure transmitting signal can be significantly reduced, thus decreasing the power consumption of the tire monitor to a satisfactory level.
However, with the third approach, it is impossible to achieve a real-time monitoring of the inflation pressure of the tire. Specifically, according to the third approach, transmission times, at which the transmitter of the tire monitor transmits the pressure transmitting signal, are determined by the receiver, not by the tire monitor. Therefore, when a notable change in the inflation pressure of the tire occurs during the time interval between any two successive transmission times determined by the receiver, the change in the inflation pressure of the tire cannot be immediately communicated to the receiver. Such a time lag in communicating the change in the inflation pressure of the tire to the receiver may result in a delay in taking a suitable measure against the change.